1. Field of the Invention
The present invention relates to an encoder, and more particularly, the present invention relates to an expansion encoder.
2. Description of Related Art
With the development of multimedia technology, digital televisions (DTVs) are capable of providing high definition image quality and preferred surround sound effect compared with conventional televisions. Moreover, the DTVs adopt digital signal transmission and compression, thus effectively utilize the bandwidth and reduce the noise interference from the outside. In terms of the processing of digital signal, the MPEG-2 encoding standard defines two data stream forms, namely, program stream (PS) and transport stream (TS).
FIG. 1A is a schematic view of a PS. Referring to FIG. 1A, the PS 100 is composed of one or more streams (e.g., streams 110, 120) containing packetized elementary stream (PES) packets taking a common time base as reference. For example, the stream 120 includes video PES packets 122 to 124, an audio PES packet 125, and a data PES packet 126, as well a header 121. The PS is deigned to be transmitted in an error-free environment and is adapted to an application of interactive multimedia. The elementary stream (ES) is an audio, a video, and a single signal (usually, a compressed signal) output by a data encoder, which becomes PES after being packetized.
FIG. 1B is a schematic view of a TS. Referring to FIG. 1B, the TS 130 is a combination of fixed-sized transport packets and the transport packets of one or more program, in which fixed-sized transport packets are formed by separating the PES packets. For example, the TS 130 includes a video transport packet 131, an audio transport packet 132, a private data transport packet 133, a service information transport packet 134, and a null transport packet 135, and so on. Each of the transport packets has a header at the front end. The PES packet constituting the elementary stream of a program takes the common time base as reference, so the transport packets in the TS can make reference to different time bases.
The data stream in the forms of PS and TS is constructed by an emitter defined by MPEG-2, so a decoder must be designed correspondingly at a receiving end to separate and decode the packets and save the packets into corresponding memory blocks. FIG. 2 is an architecture diagram of a conventional decoder. Referring to FIG. 2, a decoder 200 includes a pre-unit 210 and a plurality of data filters 220. The pre-unit 210 receives the data stream in the form of PS and TS of the emitter 250 and provides the data stream containing various transport packets to the data filters 220.
A pattern is saved in a memory of the data filters 220 to be compared with the data stream, so as to filter out desired information. The data filters 220 then save the filtered information into a system memory 230. Next, a processor 240 accesses the system memory 230 according to the requirements. Those skilled in the art would appreciate that if the number of the data filters 220 is M (M is a positive integer), the decoder 200 may save M types of patterns at most. However, if the data stream has more than M types of data, the data filters 220 cannot filter out all the desired information.
In view of the above, the conventional art adds the number of the data filters 220 to solve the above problem. However, the hardware cost is also increased.